Variable autotransformer



March 21, 1961 w. P. CARPENTER 2,976,477

VARIABLE AUTOTRANSFORMER Filed Feb. 11, 1957 6 INVENTOR. -27\ J6 lZ Z'ZZz'a/7z F Cape/256x" Z2 25 BY 2,976,477 lc Patented Mar. 21, 1961 VARIABLE AUTOTRANSFORMER William P. Carpenter, Bristol, Conn, assignor to The Superior Electric Company, Bristol, Conn., a corporation of Connecticut Filed Feb. 11, 1957, Ser. No. 639,503

2 Claims. (Cl. 323-47) The present invention relates to a variable autotransformer, and more particularly to a control unit having an autotransformer utilized for controlling the brilliancy of an electric incandescent lamp.

In my copending application, Serial No. 542,380, filed October 24, 1955, entitled Remote Electrical Control, now US. Patent No. 2,840,765, granted June 24, 1958, there is disclosed a device to which an incandescent lamp is electrically connected for controlling the degree of luminosity of the lamp from zero to maximum in minute increments. The control is effectuated by a variable autotransformer electrically positioned between the lamp and a source of electrical energy, such as a standard household electrical outlet. The autotransformer has a core with a winding thereon and provides for minute increment changes by reason of having a brush ride on a commutating surface formed on the winding so that the brush is in engagement with at least one turn of the winding substantially over the entire length of the winding. The autotransformer has a maximum rating and this rating determines the size of the bulb or bulbs which may safely be controlled by the autotransformer without excessive overheating or malfunction. The wattage or size of bulbs being more commonly used in lamps is increasing beyond the rating of the autotransformer and hence the opportunities where the autotransformer may be utilized are being severely limited.

To make the luminosity control usable safely with larger size bulbs, the rating of the autotransformer-must be increased. This may, of course, be accomplished by increasing the physical dimensions of the components of the autotransformer, such as increasing the size of the wire and the size of the permeable core. However, such a construction requires an additional complete set of manufacturing tools and equipment and also the increase in size of the control would render it less presentable or desirable to have in a household.

An approach to increasing the wattage without increasing the size is to use a larger size of wire with fewer turns on the same size of core. The larger wire is capable of handling the increased current. However, this approach is not satisfactory since the less number of turns and larger current flowing in the winding increases the flux density in the core and when used on normal 60 cycle household current produces an annoying buzzing.

Another approach is to utilize a wire tapering in diameter, that is, increasing the size progressively from one end to the other end. However, this approach is not feasible because of the extreme manufacturing difficulties and expense involved.

It is an object of the present invention to provide for a variable autotransformer having an increased rating without increasing the physical dimensions thereof and without substantially decreasing the usability of the autotransformer. I

Another object of the present invention is to provide in a variable autotransformer of the above type which is used for controlling the luminosity of electric lamps for increasing the size of the bulb which may safely be con trolled by the autotransformer without any effective diminution in the degree of control of the lamps.

In attaining the above objects, there is provided a permeable core on which a length of wire is wound. The wire is composed of two portions, one being of smaller diameter than the other. The wire is wound on the core so that the larger diameter portion forms a single layer of juxtaposed turns over substantially the surface of the core while the portion of smaller diameter is preferably wound in layers one small section. The larger diameter wire has one surface formed as a commutating surface, and may be hereinafter referred to as the commutating winding, on which a brush rides to vary the output of the autotransformer and hence the control of the brillance of a lamp.

In the embodiment shown, the smaller portion hereinafter called the exciting portion of the winding consists of approximately 10 percent of the total number of turns of the winding. By the use of the above type of construction, the rating of an autotransformer of 125 watts is increased by about 20 percent with no increase in the physical dimensions of the core though prevents the control of the output voltage ranges from about 10 percent to percent instead of zero to 100 percent. However, when the autotransformer is utilized to control an electric lamp, this change is of no consequence since the zero to 10 percent output voltage effectuates almost no light output from a lamp and thus the loss of the initial 10 percent has no practical significance. While there has been set forth a specific ratio of turns, this ratio is merely illustrative and the invention is not to be considered as limited solely thereto.

A feature of the invention resides in providing a switch having a switch mounting means positioned to be encountered by the brush carrying arm at the junction of the commutating portion and exciting portion to thereby prevent the brush from engaging the exciting portion of the winding. The switch controls the input to the autotransformer and thus current thereto is shut off at about 10 percent of the output voltage.

Other features and advantages will hereinafter appear.

In the drawing:

Figure 1 is a view showing the control device used to control a lamp.

Fig. 2 is a side view of the autotransformer.

Fig. 3 is a plan of Fig. 2.

Fig. 4 is a plan of a portion of the autotransformer with the switch removed.

Fig. 5 is a schematic diagram of the electrical connections between the autotransformer and the lamp.

Referring to the drawing, Figure l, the control device is generally indicated by reference numeral '9 and includes a variable autotransformer 10 enclosed in a casing 11. The casing is adapted to be positioned on a table 12 or other support and a conductor 13 connects the autotransformer 10 to a plug 14. The plug 14 is somewhat similar to that described and claimed in my copending application set forth above, and has prongs 15 for insertion into a standard electrical outlet 15a and in addition has a socket 16 into which a plug 17 of a lamp 18 is inserted. While there is shown a table lamp it is obvious that other lamps having electrical incandescent bulbs, such as a floor lamp, may have their brilliance controlled by the autotransformer 10. A knob 19 projects from the casing 11 and by turning the knob the degree of luminosity of the bulb is varied and set at the desired level.

, As shown in Figs. 2 and 4, the autotransformer includes a laminated toroidal core of permeable iron 20 which is preferably formed by spirally winding a thin length of iron. Two end caps 21 and 22 are mounted on the end surfaces of the core 20. Encircling the core and end caps is a windin 23 which has two parts, a commutating portion 24 and an exciting portion 25. The commutating portion 24 is formed of heavier wire, as for example, No. 29, and is wound in a single layer over substantially the entire length of the core in juxtaposed turns. The top surface of this portion of wire is milled to provide a commutating surface 26. The exciting portion 25 of the winding 23 is wound on a small segment of the core in overlapping layers in small grooves 27 formed in the top and bottom end caps.

The exciting portion 25 is formed from small wire, such as No. 34, and it has one end joined to an adjacent end of the commutating portion as -by a terminal 28 to form the continuous winding 23. The other end of the exciting portion is connected to a terminal 29 as is the other end of the commutating portion to a terminal 30.

In order to provide for variation in the output voltage, there is a brush 31 riding on and in electrical engagement with the commutating surface 26. This brush is rotatably mounted and is attached to the knob 19 by means of a shaft 31a. The construction is such that only one or two turns of the commutating winding is contacted by the brush at any position thereof. Accordingly rotation of the brush from the junction of the two windings to the end of the commutating surface varies the output voltage from about percent to 100 percent of the input voltage. If desired to have the maximum output voltage larger than the input voltage, then the terminal fail is connected to the Winding 23 at a point prior to the end thereof.

The brush is carried by an arm 33 which has a cam portion 33a, the latter engaging a normally closed switch 32. The switch 32 is mounted adjacent the junction of the two winding portions 24 and 25 on the upper surface of the core and as the cam portion 33a engages the switch 32, it serves as a stop to prevent the brush from engaging the exciting portion of the winding in addition to deenergize the input to the autotransformer. In addition, the switch includes a mounting plate 32a which is fastened onto the top end cap and this also provides a stop upon engagement by the arm 33 to prevent the brush from engaging the exciting portion 25 of the winding. The arm 33 and cam 33a are mounted on the shaft 31a for movement therewith.

As shown in Fig. 5, the input is from the prongs and one line 34 goes through the switch 32 to the terminal 29 or end of the exciting portion of the winding 23. The other prong connects to the terminal 3t and hence to the end of the commutating portion 24 of the winding, by a lead 35. The lamp is electrically connected to the output of the autotransformer by one of its prongs being connected to a socket 116 in the plug 14 and to the terminal 29 and the other prong of the lamp is connected by a lead 36 to the brush 31.

In operation for a minimum or substantially no luminosity in the lamp, the brush is positioned in the solid. line location on the commutating surface. For maximum brilliance of the lamp, the brush is moved to the dotted line position. Any position inbetween will produce a corresponding brilliance of the lamp between minimum and maximum.

In the above construction it will be noted that the heavier wire in the commutating portion 24 of the winding 23 carries the output current to the brush and hence since the wire is heavier, more current can safely flow. In addition by using two sizes of wire the same number of turns of Winding can be Wound on the core without any increase in the size of the core.

It will be appreciated that there has been set forth in the foregoing a control unit having a variable autotransformer for varying the luminosity of an incandescent lamp in which a larger size lamp can be safely controlled without an increase in size of the autotransformer. In addition there is practically no significant alteration in the ability of the autotransformer to control the lamp. This is accomplished by providing a wire of two different sizes, with the larger size being sufficiently large to safely carry the required current forming the commutating surface and in positioning it in the higher output end of the autotransformer. The winding on which there is no commutation is at the low output end of the autotransformer and this winding has substantially no effect on the control of the light since only an insignificant amount of light is given off by the lamp at very low voltages.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used without others.

I claim:

I. A control unit including a variable autotransformer for controlling the brilliance of an electric lamp between substantially no brilliance and maximum brilliance in minute increments comprising an annular core formed of permeable material; a winding Wound on the core, said winding having a commutating portion constituting approximately percent of the total number of turns in the winding and an exciting portion with the commutating portion being formed of larger wire than the exciting portion, and being wound in a single-layer of juxtaposed turns on the core, the exciting portion being wound in overlapping layers on a small portion of the core; a commutating surface formed on the commutating portion; a brush carried by a rotatably mounted arm and adapted to ride on the commutating surface in engagement with at least one turn thereof; input leads connected to the ends of the winding; output leads, one connected to the brush and the other to the input lead connected to the end of the exciting portion of the winding of the autotransformer to which a lamp is adapted to be connected; and a normally closed switch electrically connected in an input lead and mounted to be engaged by a portion of the arm when the brush is adjacent the junction of the commutating and exciting portion of the winding to deenergize the input and mechanically prevent the brush from engaging the exciting portion of the winding.

2. A control unit including a variable autotransformer for controlling the brilliance of an electric lamp between substantially no brilliance and maximum brilliance in minute increments comprising an annular core formed of permeable material; a winding wound on the core, said winding having a commutating portion constituting a substantial portion of the total number of turns in the winding and an exciting portion constituting the rest of the turns with the commutating portion being formed of larger wire than the exciting portion, and being wound in a single-layer of juxtaposed turns on the core, the exciting portion being wound in overlapping layers on a small portion of the core; a commutating surface formed on the commutating portion; a brush carried by a rotatably mounted arm and adapted to ride on the commutating surface in engagement with at least one turn thereof; input leads connected to the ends of the winding; output leads, one connected to the brush and the other to the input lead connected to the end of the exciting portion of the winding of the autotransformer to which a lamp is adapted to the connected; and a normally closed switch electrically connected in an input lead and mounted to be engaged by a portion of the arm when it is adjacent the junction of the commutating and exciting portion of the winding to deenergize the input and mechanically prevent the brush from engaging the exciting portion of the winding.

References Cited in the file of this patent UNITED STATES PATENTS 2,388,996 Preston Nov. 13, 1945 2,715,197 Dubroff et al Aug. 9, 1955 2,735,979 Coben Feb. 21, 1956 

